Rust inhibited poly(hexafluoropropylene oxide) oil compositions



United States Patent Ofifice 3,367,868 Patented Feb. 6, 1968 3,367,868 RUST INHIBITED POLY(HEXAFLUOROPRO- PYLENE OXIDE) 01L COMPDSHTIONS John Tevlin Skehan, Claymont, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Apr. 1, 1966, Ser. No. 539,314 9 Claims. (Cl. 252-34.7)

R OfCF CF CF Ol cF CF and motor CF CF oi CF CF 3 CF (CF *EOCF CF (CFa ErrOR in which R, is a perfiuoroalkyl group having 1 to about 6 carbon atoms. These oils may be tailored, if desired, to operate at temperatures as high as 800 F. They are not affected by either oxygen or moisture at these temperatures. However, rusting of ferrous metals has been encountered at these temperatures. Accordingly, it is desirable to provide inhibitors which prevent rusting of these metals at extreme temperatures.

These oils are also used to prevent rusting of metal parts at ambient temperatures. Many parts or subassemblies of devices, after being manufactured, are filled with these oils and stored until needed, often a considerable period of time. Although poly(hexafluoropropylene oxide) oils are superior to hydrocarbon oils for this use, complete rust prevention is not obtained with these oils alone.

In order to be useful with these oils, a rust inhibitor must possess a number of specific properties. First of all, it must inhibit rust. Furthermore, it must be soluble in and compatible with the oil. The solubility must be sufiicient to provide an effective amount of inhibitor in the oil, both at operating temperatures and at ambient temperatures. There must be no separation of the inhibitor from the oil even while the device containing the oil is not in use. The inhibitor itself must also possess a high degree of thermal stability at the temperatures at which the oils are used. Aninhibitor which decomposes under operating conditions will lose its effectiveness rapidly. Moreover, the inhibitor should not seriously affect lubricant properties, particularly lubricity, oil viscosity and oil viscosity index. These and other requirements eliminate most, if not all, known rust inhibitors.

It is an object of this invention to provide poly(hexafluoropropylene oxide) oil compositions containing rust inhibitors which considerably reduce or prevent rusting of ferrous metals even at extremely high temperatures. Other objects will become apparent from the following description of this invention.

It has now been discovered that reduced rusting of ferrous metals in the presence of poly(hexafiuoropropylene oxide) oils can be obtained by using a poly(hexafiuoropropylene oxide) oil composition which comprises poly(hexafluoropropylene oxide) oil of the structure R OfCF CF 3 CF 0) i CF CF or R OfCF (SP CF Oi CF CF CF (CF 3 )-EOCF CF (CF 3 550R;

where n, p and r are integers indicating the degree of polymerization and R is a perfiuoroalkyl group having 1 to about 6 carbon atoms, said oil having an average molecular weight of at least about 3,000 and a pour point not in excess of about 50 F. and, as rust inhibitor, an effective amount of perfluoroalkylether acid or corre sponding ammonium salt of the structure R O-ECF (CF CF oi CF (CF 3 )1 COOB in which m is about 7 to 18, B is H or NH, and Rf is as previously stated.

Poly(hexafluoropropylene oxide) oils of the above structures are extremely stable at elevated temperatures. Those polymers having average molecular weights of at least about 3,000 and pour points not in excess of about 50 F. are quite useful as lubricating oils. Polymers of the type R O ECF (CF CF Oi CF CF having an average molecular weight of about 5,500 to 7,000 are preferred. These molecular weight designations are based upon number average molecular weights obtained by the spectroscopic method. The pour point designation is based upon Federal Test Method Standard 791, method 351.

These poly(hexafluoropropylene oxide) oils may be prepared in several ways. Hexafluoropropylene oxide is readily homopolymerized to products of the structure cF cF CF OfCF (CE, CF O} CF CF, COF where n is 0 or an integer indicating the degree of polymerization, as described in Canadian Patent No. 725,740, issued Jan. 11, 1966. Polymers of the structure where x and y are each 1 to about 4, are prepared by polymerizing hexafluoropropylene oxide in the presence of a ketone of the structure as described in Canadian Patent No. 707,363, issued Apr. 6, 1965. Polymers of the structure F (CF CF O-fCF CF CF Oii CF (CF COF where z is 0 to about 5 are prepared by polymerizing hexafluoropropylene oxide in the presence of an acid fluoride of the formula F (CF COF RfO'ECF (CF CF OPr CF (CF COOH where R, is a perfiuoroalkyl group having 1 to about 6 carbon atoms. The acids derived from these products react with elemental fluorine according to the method of British Patent No. 1,000,802 to form These polymers also dimerize under the influence of ultraviolet light, as described in U.S. Patent No. 3,214,- 478, to form oils of the formula The rust inhibitors used in the compositions of this invention are the perfluoroalkyl ether carboxylic acids and corresponding ammonium salts of the structure in which m is about 7 to 18, B is H or NH, and R is a perfiuoroalkyl group having 1 to about 6 carbon atoms. Preferably m is about 7 to 10 and R is CF CF CF These acids are prepared by hydrolyzing hexafluoro propylene oxide polymers of the structure RHECF CF CF Oi CF (CF 3 COP as indicated above. The corresponding ammonium salts are prepared by first mixing the acid with a suitable solvent, such as toluene in which the acid partially dissolves and partially disperses in finely divided form. Ammonia gas is then bubbled through the mixture at room temperature. After all of the acid has been neutralized, the solvent is evaporated under vacuum leaving the solid ammonium salt of the acid.

The poly(hexafluoropropylene oxide) oil composition of this invention should contain an effective amount of the acid or ammonium salt as rust inhibitor. By eflective amount is meant the amount required to produce a useful inhibitor effect for the required service life of the device containing the oil at the operating temperature. The various ferrous metals differ considerably in the amount of rust which will occur and the amount of inhibitor required to prevent it. Furthermore, inhibitor is probably consumed while doing its job, hence increased service life or higher use temperatures will require larger amounts of inhibitor. Accordingly, the exact amount of inhibitor required for specific applications will vary considerably.

In general, the amount of acid or ammonium salt in the oil composition will be in the range of about 0.1 to 2% by weight. So long as at least about 0.1% of inhibitor is present, a significant amount of rust inhibition is obtained. As the amount of inhibitor is increased, a quantitative reduction in rusting is obtained up to a point. More than about 2% of inhibitor seldom produces any significant increase in effect. To prevent rusting over long periods, it is preferable to add about 1 to 2% of the acid or ammonium salt. These rust inhibitors are completely soluble in the poly(hexafluoropropylene oxide) oils in the required amounts.

The following examples, illustrating the novel oil compositions of this invention and their utility, are given without any intention that the invention be limited thereto. All percentages are by weight.

Examples 1 and 2 Oil compositions containing poly(hexafluoropropylene oxide) of the formula having an average molecular weight of 4,300 and 0.2% of an acid or ammonium salt of the structure n-C F O-ECF (CF CF OhCF (C1 COOB in which B is H or NH; are tested for rust preventing qualities using test method D-665 of the American Society for Testing Materials. Procedure B is followed using synthetic sea water. Briefly, the test consists of immersing an iron billet in a mixture of the oil composition and the 4 sea Water for 48 hours, and then examining the surface of the billet for rust.

For comparison, a control experiment in which no inhibitor is present is carried out. The following results are obtained.

TABLE Percent of Example Inhibitor Surface Rusted 1 Ammonium salt .2 0 None 45 Examples 3 and 4 Examples 1 and 2 are repeated except that the poly- (hexafluoropropylene oxide) oil is of the structure and has an average molecular Weight of 6,200. Similar results are obtained.

Although the invention has been described and exemplified by way of specific embodiments, it is to be understood that it is not limited thereto. As will be apparent to R OiECF C1 CF O-} CF CF R OiECF CF CF Oi CF CF CF (CF *EOCF CF (CF hOR;

where n, p and r are integers indicating the degree of polymerization and R, is a perfluoroalkyl group having 1 to 6 carbon atoms, said oil having an average molecular weight of at least 3,000 and a pour point not in excess 0 of 50 F. and, as rust inhibitor, an effective amount of perfluoroalkylether compound selected from the group consisting of acids and corresponding ammonium salts of the formula R O ECF CF CF oi CF (CF COOB in which m is 7 to 10, B is H or NH, and R; is as previously stated.

2. The composition of claim 1 in which the poly(hexafluoropropylene oxide) oil is of the formula and 0.1 to 2% by weight of perfluoroalkylether acid is present.

3. The composition of claim 2 in which R, is

the poly(hexafiuoropropylene oxide) oil has an average molecular weight of 5,500 to 7,000 and l to 2% of perfluoroalkylether acid is present.

4. The composition of claim 1 in which the poly(hexafluoropropylene oxide) oil is of the formula and 0.1 to 2% by weight of the ammonium salt of perfluoroalkylether acid is present.

5. The composition of claim 4 in which R; is

the poly(hexafluoropropylene oxide) oil has an average molecular weight of 5,500 to 7,000 and 1 to 2% of the and 0.1 to 2% by weight of perfluoroalkylether acid is present.

7. The composition of claim 6 in which R: is

CF CF CF the poly(hexafluoropropylene oxide) oil has an average molecular weight of 5,500 to 7,000 and 1 to 2% of perfiuoroalkylether acid is present.

8. The composition of claim 1 in which the poly(hexafluoropropylene oxide) oil is of the formula R OiECF CF CF O-Q CF (CF CF and 0.1 to 2% by weight of ammonium salt of perfluoroalkylether acid is present.

9. The composition of claim 8 in which R; is

CF CF CF the poly(hexafluoropropylene oxide) ,oil has an average molecular weight of 5,500 to 7,000 and 1. to 2% of the ammonium salt of perfluoroalkylether acid is present.

References Cited UNITED STATES PATENTS 3,242,218 3/1966 Miller 260535 15 DANIEL E. WYMAN, Primary Examiner W. H. CANNON. Assistant Examiner. 

1. A POLY(HEXAFLUOROPROPYLENE OXIDE) OIL COMPOSITION WHICH COMPRISES, AS THE BASE, A MAJOR AMOUNT OF POLY(HEXAFLUOROPROPYLENE OXIDE) OIL OF THE FORMULA 